Simple physics kinematics question?

Use the kinematic formula

Vf^2 = Vi^2 + 2*a*y

where Vf stands for final velocity, Vi (initial) = 0, a = -g = -9.8m/s^2, y = 2.45m

assume g = 10 m/s^2. 2nd stone it is thrown upward with 20 m/s velocity takes 20/g or 20/10 = 2 s to bypass up and then for coming all the way down to the comparable place it takes 2 greater seconds. After this there is not any distinction between the 1st stone and the 2nd stone because of the fact the two have 20 m/s velocity and the two are vacationing down from the comparable top. for this reason 2nd stone takes t sec greater to realize floor. for this reason 2nd stone takes in entire t+4 2nd. So option "c) t +4 sec" is authentic.

First of, 2.45 is not the "safest" height you can fall from, Unless its for a general person, but if you do parkour like me, the safest is around 5m, although Sabastian foukan jumped 11m and walked away.. yeah Im not good a physics so i cant help u there xD